Off-grid, solar home doesn’t scrimp on comfort

Off-grid, solar home doesn’t scrimp on comfort

webster, wis. — Comfort was the only demand that Michael Sperry’s wife, Judy, made when he proposed building an off-grid, solar-powered home in Northwest Wisconsin.

“She was willing to go along with my environmental experiment as long as our family wouldn’t be uncomfortable,” recalls the automotive body-repair shop owner, who selected radiant floor heating to satisfy his wife’s concerns.

Indeed, at just over 5,000-sq.ft., the four-bedroom, three-story home does not sacrifice creature comfort; nor, for that matter, electricity. Because the home generates all its electricity from solar power, everything — from mechanical systems to appliances — optimizes energy use.

In addition to fueling the home’s radiant heating system and domestic hot water, the solar photovoltaic panels provide power for all the modern appliances and amenities you would expect in a 21st century American household: washer, dryer, dishwasher, personal computer and even a 42-inch plasma television.

In fact, one of the major challenges for the project was to power the home’s heating system while using less energy than a 200-Watt light bulb. The system today exceeds this seemingly implausible goal, drawing just one-tenth of that 200-Watt target – 19 watts – thanks to a new circulator.

First introduced by Grundfos in Europe earlier this decade, the Alpha is an energy-optimized, 115V circulator that features a permanent magnet motor designed to cut power consumption by at least 50% and usually more, as compared with other circulators in its class. For Sperry, the savings went well beyond 50%.

Emphasis on energy savings

“In designing a radiant heating system for a luxury home such as this, we would normally spec 10 pumps: a primary pump, a secondary loop pump, an injection/mixing pump plus seven zone pumps,” explained heating contractor and system installer Terry Burns. “In an off-grid home, this was totally unacceptable, as it would have required roughly 900 watts of power per hour.”

To scale back the energy usage, Burns drew upon technology normally used in commercial-industrial applications. He replaced the seven zone pumps with pressure differential valves (which require no electricity) and eliminated the injection/mixing pump, as well as the secondary loop pump.

As a result, the one and only remaining pump in the system design was a single circulator to bring hot water from Sperry’s outdoor wood-burning boiler to the main manifold, where it travels throughout the home’s 9,000-ft. of Uponor PEX tubing buried in the basement slab, as well as stapled under each of the two upper floors.

But while the single-pump design performed as expected, its energy use exceeded plan and placed a significant drain on the home’s electric power, which limited use of other appliances and devices.

“The original circulator did the job, but was an energy hog,” Sperry remarked. “We have a spreadsheet showing what all of our appliances and electrical components draw throughout a normal day, and we monitor it very closely. The original pump was drawing 186 Watts continuously, and depleting our solar battery bank by roughly 15% overnight.”

System designer Burns spent months searching for an alternative, but “could not find anything that fit our parameters in terms of pump head and flow rate,” Sperry explained. “There simply was nothing suitable for this application that would reduce energy use.”

Breakthrough technology

In March 2008, Burns learned about the circulator and immediately realized that the product was his answer.

“Although the Alpha pump wasn’t yet commercially available, I knew this was the only thing out there that could solve our energy issue,” recalled Burns, who was able to get a unit to test in the Sperry home.

“The pump exceeded the manufacturer’s claims – and my wildest dreams – in every category,” said Burns, “energy use, performance [homeowner comfort] and its silent operation.”

Intended for residential and light-commercial hydronic applications, the pump features a function that automatically and continuously adjusts circulator performance to the changing needs of the heating system. The circulator will automatically find the lowest possible operating-efficiency point to meet demand, noted Burns, thereby saving both energy and money.

This winter of 2008-2009 — one of the coldest on record in the Upper Midwest — delivered a quick and dramatic payoff on Sperry’s new investment. The circulator cut electrical consumption by 90% almost immediately, without any sacrifice in personal comfort, according to Sperry, who noted: “We are accustomed to keeping our thermostat at 76°F during the coldest months.”

Meanwhile, the backup gas generator that ran for 205 hours during the winter of 2007-2008 was needed for only 86 hours this past winter, despite the colder temperatures because there was enough battery power left to keep the radiant system running. This reduced gas usage resulted in a 70% decrease in the gas bill from one winter to the next, reported Sperry, from $565 to $170. Moving forward, Sperry estimated he’ll use his generator for just 50 hours, as he becomes more familiar with the system’s operation.

“We couldn’t be happier with the Alpha’s performance. We’ve had no problems at all, and the pump is virtually silent, which is heaven compared with the obnoxious hum that reverberated throughout the house from the previous pump.

“I talk with a lot of off-grid people about the heating systems we all use,” Sperry continued, “and they warned me that my biggest headache would be the water-circulating pump, because it typically uses so much energy. But the Alpha has proven to be an absolute dream. For any homeowner who wants to move off-grid or simply to maximize energy efficiency, this is the best way to go.”

TAGS: Solar